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STACEE status report

Presented to SAGENAP panel,April 15, 2004

Washington, DC

K. RaganMcGill University, Montreal

for the STACEE collaboration

- Presentation of experiment- Science issues & goals- Detector status- Recent results- Outlook/Conclusions

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Presentation of Experiment

• STACEE is based at Sandia National Labs, Albuquerque NM

• uses 64 heliostats of the National Solar Thermal Test Facility (NSTTF) and custom secondary optics to capture Cherenkov light on PMT cameras

Size of heliostat field well matched to Cherenkov footprint on ground:

~250 m

(HESS diagram)

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Presentation of Experiment

• NSTTF is a user facility and we incur costs to be present and active there. Currently costs are approx. $100/hour for heliostat usage;

• Heliostats are well maintained; time lost to malfunctioning is small (although non-zero!)

• Currently retro-fitting heliostats with more rapid motors for GRB response.

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Presentation of Experiment

tessellated secondary (1.9 m diameter)

Three 1.9m secondaries on 260’ level have 16-PMT cameras

PMT ‘camera’

Two 1.1m secondaries on 220’ level have 8-PMT cameras

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• custom delay & trigger electronics designed to capture events in programmable window (8-16 ns)

• full FADC waveform digitization on each channel at 1 GHz (more later)

Presentation of Experiment

Commercial (Acqiris) FADC modules (4 channels per board)

custom delay/trigger (8 channels per board)

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• Also dedicated atmospheric monitoring station, with:– PMT-based photometry– CCD for autoguiding– infrared radiometers– weather station

• data stream: 64 waveforms containing full timing and amplitude information, plus:– GPS timestamp– PMT currents & rates– Heliostat position data– Atmospheric monitoring data

Presentation of Experiment

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Presentation of Experiment

• Due to large mirror area, STACEE achieves lower energy threshold than imagers & is sensitive below 100 GeV

• This will continue to be an important niche in the early VERITAS/GLAST era

Simulation of response to Crab flux:

“threshold”

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Presentation of Experiment

The STACEE Collaboration:• Alberta: Gingrich + 1 MSc student• Barnard/Columbia: Mukherjee + 1 PhD student• Case Western: Covault + 2 post-docs (Driscoll, Colombo)• McGill: Hanna + Ragan + post-doc (Kildea) + 4 students (3 PhD,

1 MSc)• UCLA: Ong + research scientist (Zweerink) + 2 PhD students• UCSC/SCIPP: Williams

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Presentation of Experiment

STACEE Milestones: • 1997: SAGENAP presentation; first STACEE funding• 2000: detection of Crab nebula with 32-channel instrument at

190 GeV threshold (ApJ 547, 949 (2001))• 2001: detection of Mrk421 flare with STACEE-48 (ApJ 579, L5

(2002))• 2002: full STACEE-64 commissioned • 2003: WComae upper limit at ~130 GeV threshold (ApJ in

press)• 2004-2006(7) Continued operations

Results published in ApJ and ApJL, as well as numerous conference proceedings. Three technical papers in NIM.

Four PhD’s, four MSc’s graduated; 6 more PhD’s + 2 MSc’s in pipeline; numerous undergraduates trained.

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Science Issues and Goals

STACEE targets are primarily AGNs, pulsars, GRBs; but also EGRET UnIDs. Some clear questions:

• AGN:• nature of primary particles (leptonic or hadronic?)

F. Halzen

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Science Issues and Goals

• exploration of EBL absorption effects, primarily through multi-wavelength campaigns

Abso

rpti

on e

xp(-

tau)

Energy

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Science Issues and Goals

• pulsars:• energy of cutoff of pulsed component (polar cap vs. outer gap)?

• GRBs:• maximum energy of burst emission• luminosity and energy evolution during afterglow

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Science Issues and Goals

STACEE can address all of these issues with its unique sensitivity at E<100 GeV !

• EGRET UNIDs:• most EGRET sources are unidentified• huge potential here for study: for example, recent HEGRA observation of TeV2032 may be archetype of cosmic ray ‘nursery’

HEGRA (Astron. Astrophys. 393 (2000) L37

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Detector Status

Current status:• STACEE-64 fully constructed by late 2001• FADCs fully installed in late spring 2002• first full season with complete detector

configuration: 2002-2003• large data samples on AGNs, Crab• Crab optical pulsar observed to confirm timing• still on learning curve with FADCs:

• padding to account for field darkness differences• in-situ gain measurements• advanced reconstruction techniques

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Detector Status

Crab pulsar is an exciting target in STACEE energy regime;

• we took special data to observe optical pulsar and confirm absolute timing;

(HST data) light pollution @ 120 Hz

non-Cherenkov data filtered to remove high-freq components

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Detector Status

• digitize PMT anode current at 10 kHz, GPS time stamp periodically, fold at known ephemeris of Crab

STACEE phase diagram

STACEE phase diagram (simulation)

Observation of optical pulsar confirms both absolute timing and optical throughput

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Detector Status

FADC information vastly more powerful than previous TDC + ADC combination, and we are still on learning curve here:

discriminatorthreshold

nominal trigger position

One channel

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Detector Status

Average On-Off current difference

Stars (no excess expected)Eg, padding to account for

field darkness differences:• excess night sky background (due to

different star fields) in ON or OFF can compromise ON/OFF comparison: can mimic signal or hide it, by promoting sub-threshold events;

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Detector Status

• excess light leads to larger current, and to larger variance of ‘baseline’ in AC-coupled PMT traces

• critical to correct for this with ‘padding’: adjustment of lower light data by addition of noise;

• so make library of NSB pulses;• catalogue them as a function of

variance (aka current);• use them to ‘pad’ lower-light-level

data to variance/current of noisier data

• FADC data are essential• it works !

Quality cuts only Library PaddingStar "source" ON OFF Excess ON OFF Excess

iota CrB 75505 73060 10.99 52423 53367 1.0221 Com 32354 31299 6.16 22859 23269 -0.23HIP 89729 74823 73292 5.03 53463 53678 0.88

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Detector Status

off-source trace

+ NSB library trace

=

padded trace

on-source trace

Do this channel-by-channel;then reimpose trigger and dodirect on-off comparison

Schematically:

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Detector Status

Advanced reconstruction techniques using full waveform information also promise superior directional and energy reconstruction:

Assuming shower core at array center

Using full waveform information to reconstruct shower core

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Detector Status

Both 2002-2003 and 2003-2004 seasons concentrated on detector studies, Crab, and AGN data:

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Detector Status

Details for current 2003-2004 season:Source RA Optimal Type z Comments Pairs Status3C66A 02h23m Oct AGN 0.444 a) 70 Complete; analysis ongoingCrab 05h34 Nov/Dec SNR b) 68 Complete; analysis ongoingOJ+287 08h54m Jan AGN 0.306 c) 27 OngoingMrk421 11h04m Feb/Mar AGN 0.031 d) 25 Limited observations if flaringW Comae 12h21m Mar AGN 0.102 e) 25 OngoingH1426 14h28m Apr AGN 0.129 f) 18 OngoingMrk501 16h54m May AGN 0.033 g) - Upcoming; limited unless flaringGRBs - - GRB - h) On GCN alerts

a) EGRET source; extreme BLL; multi-wavelength campaign with RXTE & VERITAS as well as lower – first such comprehensive broadband campaign to our knowledge; contemporaneous data will provide input to modelers; higher z, so possible EBL information;

b) Standard Candle; pulsar energy limit & spectrum both worthy goals;c) EGRET source, with moderate z, C&G predictions; best source available in this RA range;d) Well studied, EGRET source; detected by ACT incl. STACEE; useful for instrument studies if

flaring and contemporaneous data with VERITAS;e) Hard EGRET spectrum; LBL; well-measured in X; detailed predictions for both electronic SSC

and proton models;f) XBL, not EGRET source; TeV flux predicted from X-ray data, found by ACT, g) Similar to Mrk421, likely data if in flaring state.h) Predictions: ~7 prompt follow-ups per year in SWIFT era. GRB @ 100 GeV would be seminal !

Active participation in multi- campaigns, ToOs, GCN alerts

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Detector Status

GRB data acquired:

GRBUTC Time

SpacecraftNotice Delay

(minutes)

Time until Observable by

STACEE (hours)STACEE Observations

021004 12:06:14 HETE 0.8 14.1 None

021112 03:28:16 HETE 81 3.2 Starting 219 minutes after burst ;112 minutes on burst position

021211 11:18:34 HETE 0.4 0.0 None; bad weather

030115 03:22:34 HETE 71 8.4 None; full moon

030227 08:42:16 INTEGRAL 48 17.7 None

030324 03:12:43 HETE 0.4 2.0 Starting 123 minutes after burst; 56 minutes on burst position

030328 11:20:58 HETE 53 16.7 None

030329 11:37:15 HETE 73 15.2 None

030417 06:24:20 INTEGRAL 0.2 >24 None

030418 09:59:19 HETE 3.6 17.2 None

030501A 03:10:19 INTEGRAL 0.3 4.6 Starting 369 minutes after burst; 28 minutes on burst position

030519 14:04:54 HETE 0.6 Infinite None

030528 13:03:03 HETE 0.6 17.6 None

030722 11:02:46 INTEGRAL 0.2 >24 None

030723 06:28:18 HETE 0.8 Infinite None

030824 16:47:35 HETE 60 11.7 None

030913 17:06:58 HETE 0.6 9.9 None; full moon

031015 19:23:46 INTEGRAL 0.2 >24 None

Bursts from 9/01/02 through 10/31/03 with alert within 90’ of burst

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Detector Status

Other, more speculative sources possible in future:Source RA Optimal Type z Comments0430+428 04h33m Nov AGN unknown a)1835+5918 18h35m June EGRET UnID b)PSR1951 19h53m Jun/Jul pulsar c)1959+650 20h00 Jun/Jul AGN 0.048 d)TeV2032 20h36m July OB assoc? e)2200+420 22h00m Aug AGN 0.069 f)2344+514 23h47m Sept AGN 0.044 g)

a) EGRET source with photons > 30 GeV; AGN at unknown redshift; competes with Crab;

b) Most persistent EGRET UnID; Chandra X-ray position; postulated Geminga-like (radio-quiet) pulsar;

c) EGRET pulsar; SNR CTB80;d) Non-EGRET; XBL; C&G TeV flux predictions e) First TeV-discovered source; extended & confused region; possibly OB-association,

postulated as archetype of cosmic-ray production regions;f) Low z EGRET source; IBL; “3C66A-like”; not seen by ACTs;g) Non-EGRET AGN, seen by ACTs; XBL; “421-like”; spectrum measurement desirable.

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Recent Results

W Comae (aka ON+231):• z=0.102 EGRET blazar with hard spectrum, consistent with power law of a=1.73 +/- 0.18;• undetected by imagers (at E>300 GeV);• extensively studied at X-ray energies;• nice test case for leptonic vs hadronic models of blazar emission:

• leptonic models predict emission cuts off below ~100 GeV;• hadronic models allow emission to significantly higher energies;

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Recent Results

W Comae data:• STACEE acquired data on WComae in Mar-Jun 2003:

• 34 ON-OFF pairs, 13.5 ON-source hours• after quality cuts on heliostat pointing, stability of L1 trigger rates, and DAQ performance: 10.5 hrs ON-source;• raw ON-excess at 4.6 level; but typically 1-2 mA current excess in ON data;• library padding reduces ON excess to 0.88 , consistent with no emission;• derived 95% UL on flux is typically • ~0.5-1.0x10-10cm-2 s-1

• at threshold energy of ~130-160 GeV • result accepted for publication in ApJ, ~June 2004

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Recent Results

Resulting upper limits:

proton synchrotron models, with low and high EBL absorption

EGRET power-law

STACEE data is startingto constrain models

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Recent Results

1H1426+428:• z=0.129 BL Lac;• unobserved by EGRET;• detected by imagers (HEGRA, CAT, Whipple) at E>300 GeV, data consistent with power law (a = 3.5);

• STACEE took 22 ON/OFF pairs in Apr-July 2003:• 10 ON-source hours in raw-data;• 7.5 ON-source hours after quality cuts (helios + L1);• no padding done (ON-OFF current diff. < 0.5 mA);• 2.9 excess ON-source;• this data will be start of large multi-yr data set on 1H1426+428

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Recent Results

Resulting upper limit (preliminary):Petry et al. 2002

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Recent Results

These results already constrain some EBL absorption models:

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Outlook/Conclusions

• STACEE is fully operational: taking data, doing science;

• We continue to improve our understanding of the data and the power of the FADC system;

• Many sources still to be investigated in STACEE’s unique energy regime;

• Normal operations will continue until mid-2006 to the threshold of the VERITAS/GLAST era;

• Further running beyond mid-2006 will be contingent on STACEE results and evolution of VERITAS/GLAST.